The root beer was better in 1958

The flavor was "fuller." probably because they made it from real roots, instead of chemicals. (but did you know that the oil from the sassafras root is a carcinogen?)
he stayed long enough for a root beer and a couple of conversations, then returned. He can't stop thinking about it. He can't help thinking that it can't have been real -- that it must have been a dream.
he can't stop thinking about what Al is asking him to do.
"Did I want to spend years in the past? No. But I did want to go back. If only to hear how Little Richard sounded when he was still top of the pops. Or get on a Trans World Airlines plane without having to take off my shoes, submit to a full body scan, and go through a metal detector. And I wanted another root beer."